1. Field of the Invention
The present invention relates to orthopedic devices for injured knees, and it relates more particularly to a knee brace adapted to serve as an external replacement or substitute for a torn anterior cruciate ligament.
2. Description of the Prior Art
The human knee is a very complex mechanism that is highly vulnerable to injury in various sports, particularly such contact sports as football, soccer and basketball. The primary front/rear locating means within the knee joint is a pair of crossed ligaments called the cruciate ligaments which connect between the femur and the tibia. These are the anterior and posterior cruciate ligaments. The anterior cruciate ligament controls forward drawer shifting or translocation of the tibia relative to the femur, while the posterior cruciate ligament controls rearward drawer shifting or translocation of the tibia relative to the femur. By far the most commonly injured of the cruciate ligaments is the anterior cruciate ligament, torn anterior cruciate ligaments being a major crippler of athletes involved in contact sports. Heretofore, an athlete having a torn anterior cruciate ligament was generally not able to continue athletic performance without corrective surgery, and even then 100 percent rehabilitation was not likely.
Applicants are not aware of anyone having heretofore specifically addressed the possibility of an external substitute or replacement for a torn anterior cruciate ligament in the form of an orthopedic device, and none of the many knee orthotics of which applicants are aware was or is capable of compensating for an anterior cruciate ligament tear sufficiently for athletic performance.
Applicants have determined that in order for a knee brace to be effective as a substitute or replacement for a torn anterior cruciate ligament, it must include a leverage system capable of applying a strong differential force anteriorly to the femur and posteriorly to the tibia proximal the knee joint, yet none of the prior art knee braces of which applicants are aware are directed to the application of such differential force, or are in any way capable of applying the leverage necessary to achieve such differential force.
One of the factors applicants have found to be desirable in achieving the necessary leverage for a satisfactory external substitute for a torn anterior cruciate ligament is the use in the substitute brace of hinges on both the lateral and medial sides of the knee that are both bicentric and geared. Examples of such bicentric, geared hinges in knee orthotics are found in U.S. Pat. No. 4,381,768 to Erichsen, and U.S. Pat. No. 4,372,298 to Lerman. Other examples are seen in two prior U.S. patent applications in which applicants are joint inventors, Ser. No. 474,004, filed Mar. 10, 1983 for Articulating Graphite Knee Stabilizer, and Ser. No. 657,356, filed Oct. 3, 1984 for Athletic Knee Protector. Applicants said Application Ser. No. 474,004 disclosed pinion stops associated with the hinge gears for limiting the extent of flexion and extension. Another form of polycentric hinge that was not geared but had a similar action was disclosed in Cummins U.S. Pat. No. 4,245,629. Despite the presence of such bicentric hinges with geared or gear-like connections in these prior knee orthotics, none of them had a structural arrangement capable of applying leverage which would produce a force couple on the femur and tibia proximal the knee joint such as would simulate the force of a healthy anterior cruciate ligament.
Applicants are aware of another group of prior art knee orthotics having polycentric hinges that did not have geared or gear-like connections, and that also were incapable of applying leverage which could produce the necessary differential force to serve the function of an anterior cruciate ligament. These devices are disclosed in U.S. Pat. Nos. 2,467,907 to Peckham, 3,901,223 to May, Reissue 30,501 to Almeida, 4,249,524 to Anderson, and 4,271,831 to Deibert.
Applicants are also aware of a number of knee brace-type devices which utilize only single-pivot hinges, and like the other devices referred to above, none of these are capable of applying leverage that would produce a force couple corresponding in effect to the anterior cruciate ligament. Such devices are shown in U.S. Pat. Nos. 2,144,641 Snyder, 3,817,244 Taylor, 4,088,130 Applegate, 4,320,747 Daniell, Jr., and 4,353,361 Foster.
The basic purpose of all of this large number of prior art knee brace-type devices is simply to increase the stability of an injured knee, and for the most part such devices have simply constituted supplemental hinge structures strapped to the thigh and calf, intended to give added mechanical pivot strength to the knee.
Most of these prior art devices involve straps that completely and tightly encircle the leg above and below the knee in such a way that any force that may incidentally be applied in a direction to aid the anterior cruciate ligament would be generally cancelled by an opposite force. Such leg-encircling straps, to have any substantial effect in increasing the general stability of the knee, must generally be tightened to the point where they are likely to interfere with blood circulation.
In addition to their general function of stabilizing the knee, the leg-encircling straps characteristically used in prior art knee braces helped to resist the tendency of all such devices to migrate downwardly along the leg in use, both from the effects of gravity and because of the general tapering of the leg. Nevertheless, even with full leg-encircling straps, such prior art devices all had a general tendency to migrate downwardly along the leg, particularly if they were used during the rigors of athletic performance.